I've tried to imagine how such a feature could evolve naturally, and I can't really see how. I believe the impression is that it was an evolutionary feature tha

I've tried to imagine how such a feature could evolve naturally, and I can't really see how. I believe the impression is that it was an evolutionary feature that came about because they were constantly losing major organs. BUT there is quite a bit of genetic engineering and manipulation in Star Trek. Most of it is to remove genetic birth defects, but there was an entire arc in Enterprise about how a large population of Klingons were genetically altered to give them superior strength and skills. So it's possible that it was related to this, or was engineered at some point in a similar fashion. The whole arc was only to explain why the Klingons looked different in the early series and movies. Berman and Braga tried their best to keep the canon intact, and to have it make sense.